The invention concerns a method for the reduction of the carbon black content in the waste gas of a diesel engine and a device to carry out this method.
As in the past, the emission of carbon black and NO.sub.x represents one of the greatest problems of the diesel engine. All previous strategies for the reduction of pollutants exhibit a "see-saw" effect between the carbon black and NO.sub.x waste gas concentration. By a time shift of the beginning of the injection in the direction of a later injection, it is possible to reduce the formation of carbon black, but this leads to higher NO.sub.x emissions. The waste gas recycling method, on the other hand, makes possible a reduction of the NO.sub.x production by the lower temperatures in the engine, but involves a strongly increased carbon black emission.
By additional injection of water into the combustion chamber, it is possible to reduce the NO.sub.x formation by reducing the combustion temperature--see Amin Velji et al., MTZ Motorentechnische Zeitschrift 57 (1996) 7/8, 400-407. A simultaneous reduction of the carbon black emission is attained only if water in the form of a diesel-water emulsion is introduced into the combustion chamber, but not if water is introduced into the combustion chamber with the combustion air or directly by a stratified injection.
From European Patent No. B 0,333,704, a method is known for reducing the fraction of harmful substances in the waste gas--namely CO, HC, and NO.sub.x --of a combustion process, in which hydrocarbon compounds participate, by supplying a liquid composition which contains a peroxide, such as hydrogen peroxide or another peroxy compound and water, into the combustion process--with the combustion air and/or the fuel-air mixture. The supply to the combustion process takes place in that known method already during the introduction or within the ignition phase of the combustion process. A carbon black reduction in the waste gas cannot be attained in the method execution indicated in this document. The liquid composition can contain 10 to 80 vol % hydrogen peroxide, which decomposes into OH radicals in the combustion chamber, which, in turn, favor the combustion.